Electric welding torch oscillator and guide

ABSTRACT

A welding head clamping and oscillating assembly is disclosed for use in a welding machine having means for supporting and moving the assembly along a joint to be welded. The assembly includes a support platform connected to the assembly supporting means of the welding machine and a support plate slidably mounted on the support platform for reciprocal movement in a direction transverse to the joint to be welded. A welding head clamp is pivotally mounted on the support plate for arcuate oscillating movement in a direction substantially parallel to the direction of the slidable mounting of the support plate and a reversible stepping motor is operatively connected to the clamp for oscillating the clamp about its pivot axis. An electrical control circuit is also provided for the stepping motor and includes logic circuitry for producing a pulse signal at a predetermined frequency and a binary counting circuit for counting a predetermined number of pulses from the signal and producing an output signal when the predetermined number of pulses is counted. The circuit includes means responsive to the output signal and operatively connected to the motor to drive the motor alternately in first and second directions in response to successive output signals from the binary counter thereby to oscillate the welding head clamp assembly about its pivot axis.

United States Patent [1 1 Gwin et al.

[451 July 24, 1973 1 ELECTRIC WELDING TORCH OSCILLATOR AND GUIDE [75]Inventors: Richard B. Gwin, Arlington; William L. Ballis, Hilliard;Claude W. Churchheus, Laurelville; Bruce L. Hutt, Valley View, all ofOhio [73] Assignee: Columbia Gas System Service Corporation, Wilmington,Del.

[22] Filed: Oct. 14, 1971 [21] Appl. No.: 189,175

Primary Examiner-J. V. Truhe Assistant Examiner-L. A. SchutzmanAttorney-Harold L. Stults and Curtis, Morris & Safford et a].

57 ABSTRACT A welding head clamping and oscillating assembly isdisclosed for use in a welding machine having means for supporting andmoving the assembly along a joint to be welded. The assembly includes asupport platform connected to the assembly supporting means of thewelding machine and a support plate slidably mounted on the supportplatform for reciprocal movement in a direction transverse to the jointto be welded. A welding head clamp is pivotally mounted on the supportplate for arcuate oscillating movement in a direction substantiallyparallel to the direction of the slidable mounting of the support plateand a reversible stepping motor is operatively connected to the clampfor oscillating the clamp about its pivot axis. An electrical controlcircuit is also provided for the stepping motor and includes logiccircuitry for producing a pulse signal at a predetermined frequency anda binary counting circuit for counting a predetermined number of pulsesfrom the signal and producing an output signal when the predeterminednumber of pulses is counted. The circuit includes means responsive tothe output signal and operatively connected to the motor to drive themotor alternately in first and second directions in response tosuccessive output signals from the binary counter thereby to oscillatethe welding head clamp assembly about its pivot axis.

23 Claims, 13 Drawing Figures ELECTRIC WELDING TORCH OSCILLATOR ANDGUIDE This invention relates to automatic welding processes and inparticular to a welding head clamping assembly for oscillating a weldinghead with respect to a seam or joint being welded.

Oscillation of welding heads, and in particular arcuate oscillation ofthe welding head or torch across a seam to be welded", has been found toprovide a better finished weld since the head is thereby moved moreuniformly. Such oscillating patterns are useful in both butt joints orweld overlap applications, and as a result there has been an increaseduse of welding torch oscillators in the welding industry.

The increasing use of automation in the welding field also has increasedthe need for reliable methods in automatically oscillating weldingtorches during the welding process. Further, in the last several years,welding travel speeds, in automatic arc welding processes, haveincreased substantially, thereby resulting in the need for higherwelding torch oscillating speeds. As a result of these factors, andsince it is desirable to automate the welding process completely, theneed has arisen for a welding torch oscillator which can be controlledremotely or automatically by electrical circuitry.

A number of welding torch oscillators are commercially available todaythat have not completely satisfied the needs of the welding industry.Most of these commercial oscillators have mechanical linkages which aresubject to rapid wear. Such worn linkages can cause errors in thecenterline of oscillation of the torch with respect to the joint andalso deviations in the width of oscillation. Further, some of thepresent oscillators do not have the capability of oscillating at highenough speeds for use with high weld travel speed processes. Typically,such oscillators consist of a variable speed motor connected bymechanical linkages to the welding head to change the rotating motion ofthe motor to a straight line motion of the torch. The width of thestraight line oscillation is usually controlled manually by adjustingthe appropriate linkage section. Such systems are, therefore, notsuitable for automated processes.

It is also desirable in automatic processes to maintain the centerlineof the welding head oscillation in alignment with the centerline of thejoint being welded. It

often occurs that the end planes of the pipes forming the joint beingwelded are not perpendicular to the longitudinal axis of the pipes orthat the pipe diameters are not exactly the same. Therefore, if anautomatic welding machine is placedon the two pipe joints, the travelplane of the fixed welding heads will not be parallel to the weldinggroove and so it is necessary for the welding head to be tracked withthe joint during an automated'welding process.

Accordingly, it is an object of the present invention to oscillate awelding torch head during a welding process while simultaneouslytracking the head with respect to the joint being welded.

Another object of the present invention is to oscillate a weldingtorchin an automatic and accurately controlled manner with a relativelysimple electromechanical system.

Yet another object of the present invention is to provide a weldingtorch oscillator which is relatively simple in construction, inexpensiveto manufacture and efficient in operation.

It is another object of the present invention to provide a welding torchoscillator head wherein the width, frequency and centerline of theoscillations can be varied automatically by the operator for differentweld passes.

In accordance with an embodiment of the present invention a weldingtorch clamping and oscillating assembly for use in a pipeline weldingmachine having a ring gear for supporting and moving the assembly alonga joint between two pipes to be welded, is provided which includes asupport platform and means for connecting a support platform to the ringgear of the welding machine. A support plate is slidably mounted on thesupport platform for reciprocal movement in a direction transverse tothe joint to be welded and a pivot shaft is rotatably mounted in thesupport plate and extends generally perpendicularly thereto. A spur gearis rigidly secured to the pivot shaft and a reversible stepping motor isoperatively connected to the spur gear by a worm gear mounted on itsoutput shaft to oscillate the pivot shaft about its axis of rotation. Awelding torch clamp is rigidly connected to the pivot shaft for arcuateoscillation therewith in a direction substantially parallel to thedirection of sliding movement of the support plate. I I

A guide arm is mounted on the support plate and extends from the plateto a position below the support platform. The guide arm has a guidemember adapted to be positioned in the joint to be welded and located onthe guide arm in a position to be in a common plane with. the tip of awelding head mounted in the clamp when the clamp is at the central pointof its path of oscillation. The guide member tracks in the joint to bewelded as the assembly is moved therealong by the ring gear, to move thesupport plate and thus the welding torch clamp with respect to theplatform in response to variations in the lateral location of the joint,so that the welding head will oscillate with equal amplitude on eitherside of the joint. This embodiment of the invention is adapted for usein a number of welding processes and in particular it is contemplatedthat the apparatus can be used to perform the root and filler passes inthe automatic pipeline welding method described and claimed in US.Patent application Ser. No. 118,449, filed Feb. 24, 1971 and commonlyassigned herewith. The disclosure of that application is incorporatedherein by reference. 3 i

In another embodiment of the invention, which is adapted for use inthecap pass of the welding process, that is, the pass wherein the jointis substantially filled with weld metal so that his not feasible totrack the welding head during the-pass, the guide arm is eliminated anda rack gear is mounted on'the support platform for cooperation with aselectively operable reversible electric motor mounted on the supportplate and geared to the rack. By selective operation of the electricmotor, the relative position of the support plate with respect to theplatform may be adjusted so that the welding tip is centered withrespect to the joint at the beginning of the welding operation and heldby the motor in that fixed position during the welding process.

The above, and other objects, features and advantages of this invention,will be apparent in the following detailed description of illustrativeembodiments thereof, which are to be read in connection with theaccompanying drawings, wherein:

FIG. 1 is a schematic representation ofa specific embodiment of anapparatus constructed to perform in accordance with the presentinvention and mounted on a welding machine adjacent to a joint to bewelded;

FIG. 2 is an enlarged view taken on line 2-2 of FIG. 1 illustrating aportion of the mounting mechanism connecting the welding head assemblyto the welding machine;

FIG. 3 is a side view of the apparatus taken on line 3-3 of FIG. I;

FIG. 4 is a plan view of the apparatus illustrated in FIG. 3;

FIG. 5 is a schematic perspective view, with parts removed, of theapparatus illustrated in FIG. 3;

FIG. 6 is an enlarged side view of the welding torch clamp utilized inthe assembly of the present invention; FIG. 7 is a sectional view takenon line 77 of FIG.

FIG. 8 is a schematic block diagram of the electronic control circuitfor the stepping motor utilized in the assembly of the presentinvention;

FIG. 9 is a side view of a welding head clamping and oscillatingassembly in accordance with another embodiment of the present invention;

FIG. 10 is an enlarged perspective view similar to FIG. 5 of theassembly illustrated in FIG. 9;

FIG. 11 is a bottom view of the apparatus illustrated in FIG. 9;

FIG. 12 is a schematic representation of a welding machine in which thewelding head clamp of FIG. 9 is utilized; and

FIG. 13 is a sectional view taken on line l3l3 of FIG. 12.

Referring to the drawing in detail, and initially to FIG. 1 thereof, itwill be seen that a welding head clamping and oscillating assembly 10,is shown mounted in position to weld two pipeline sections 11 and 12meeting at a joint 13.

The assembly 10 includes a connecting mechanism 14 by which the assemblyis mounted on a ring gear 16. The latter is driven about the peripheryof the pipeline 1] by an electric motor 18 through its shaft 20 and apinion gear 22 mounted thereon and engaged with ring gear 16. In thismanner the assembly 10 is movable about the circumference of thepipeline during the welding operation. The ring gear is capable ofmovement along the length of the pipeline in any conventional manner inorder to move the assembly 10 to successive weld joints after completionof a welding operation.

Mounting mechanism 14 includes a pair of plates 24 and 26 which connectassembly 10 to ring gear 16 and yet permit relative movement betweenassembly 10 and ring gear 16 in a radial direction with respect to thepipes 11 and 12. Plate 24 is rigidly connected by bolts 28 (Figures), toring gear 16 and includes a dove tail flanged surface 30 on the sidethereof opposite ring gear 16. Flange 30 is received in and cooperateswith a complementary dove tail recess 32 in plate 26 and as a result,the assembly 10 is held adjacent ring gear 16, but may be slidably movedwith respect thereto in a radial direction. Such movement is limited byan adjustment and biasing mechanism 34 which includes a rod 36 having ahandle 38 at one end thereof and threaded free end portion 40. Rod 36extends in a generally radial direction with respect to ring gear 16,through a boss 42 secured inrecess 43 of flange 30 and is slidablymovable therein. A nut 44 is threadedly engaged on threaded end portion40 of rod 36 in spaced relation to the tip 46 thereof. A compressionspring 48 is engaged between boss 42 and nut 44 to bias rod 36downwardly, as seen in FIG. 2, while permitting relative movementbetween the rod and plate 24. A stop 41 is provided on rod 36 on theopposite side of boss 42 from spring 48 and adjacent handle 38 to limitthe downward movement of the rod with respect to the plate 24 under theinfluence of spring 48. End 40 of rod 36 is threadedly engaged in a boss50, see FIG. 4, secured to plate 26. As a result, it is seen that plate26 is also urged downwardly with respect to plate 24 by spring 48. Theamount of force applied to plate 26 is, of course, a function of theposition of nut 44, and the initial position of plate 26 and thusassembly 10 with respect to plate 24 and ring gear 16 may be varied byrotation of wheel 38, providing wheel 54 does not come in contact withpipe 11.

A support platform 52 is rigidly secured to plate 26 and is thus biasedradially downwardly with that plate by spring 48. A wheel 54 isrotatably mounted on a shaft 56 in support platform 52 along an axiswhich is generally perpendicular to the axis of rod 36. Thus, the axisof rotation of wheel 54 is on a radial line with respect to ring gear 16and the pipe 11. The wheel is urged into contact with the surface ofpipe 11 by the downward bias of spring 48 and facilitates the movementof the assembly along the surface of the pipe during the weldingoperation. It is noted that by the specific location of the axis ofrotation of the wheel and its point of contact with the pipe along aradial line, the possibility of tilting or jamming of the assemblyduring movement along the pipe is avoided.

A housing 60 (FIGS. 1 and 4), including a bottom support plate 62, ismounted on support platform 52, which is a hollow generally rectangularmember, for sliding reciprocal movement with respect to the platfonn ina direction transverse to the joint 13 to be welded. This is achieved bythe provision of parallelly arranged cylindrical rods 64 mounted withinplatform 52. A pair of bearing members 66 are secured to the lowersurface of plate 62 (see FIG. 5) and receive rods 64 therein to permitsliding movement of plate 62 with respect to the rods and supportplatform 52. This sliding movement of the present invention, as is morefully described hereinafter, is utilized to permit tracking of theassembly with respect to joint 13.

A pivot shaft 68 is rotatably mounted in plate 62 in any conventionalmanner. Shaft 68 extends in a generally perpendicular verticaldirection, as seen in FIGS. 3 and 5, from plate 62 and has a spur gear70 rigidly mounted thereon. A conventional stepping motor 72, Le. amotor which turns through a discrete angular movement upon theapplication of a signal or pulse, is also mounted on plate 62 andincludes a drive shaft 74 having a worm gear 76 thereon mounted inposition for meshing engagement with spur gear 70. Motor 72 iscontrolled by an electronic circuit, more fully described hereinafter,to oscillate its shaft over a predetermined range and thereby oscillateshaft 68 about its pivot axis.

A welding head clamp assembly 78 is rigidly secured to shaft 68 andoscillated with the shaft under the influence of motor 72. Clampassembly 78 is adapted to secure a welding head or torch 80 therein andhold the torch in a predetermined fixed position with respect to theweld joint 13 during the welding operation. The assembly includes afirst mounting portion 82 which has a split ring collar 84 formedintegrally therewith along its back edge 86. Split ring collar 84receives and surrounds pivot shaft 68 and is clamped thereto by means ofa bolt 88 extending between the split portion of the ring, as seen inFIG. 7. The forward edge 90 of member 82 includes a generallyrectangular recess 92 therein which is adapted to receive the secondmounting portion 93 of the clamp assembly.

Member 93 is pivotally connected to member 82 by pivot pin 94 adjacentthe top of the assembly. The rear portion 96 of member 92 has aconfiguration which is generally complementary to recess 92 and isreceived in the recess in the closed configuration of the assemblyduring the welding operation. The forward edge portion 98 of member 93includes a splitring clamp 100 in which welding head or torch 80 isreceived. A pair of bolts 102 extend between the ears 104 of collar 100to provide a clamping action of the sides of the collar against thetorch 80 in a conventional manner.

Members 82 and 93 are held in their closed configuration, seen in FlGS.3-5, by a clamping mechanism which includes a bolt 106 extending betweenthe sides 108 of member 82 which define recess 92. Bolt 106 has athreaded end portion 110 threadedly engaged with a nut 112, as seen inFIG. 7. To enhance the clamping action of this bolt assembly, the sides108, in the area of theapertures 114 through which bolt 106 extends, maybe formed at a thinner dimension than the remainder of member 82 so thatthey are somewhat flexible to give" and thus more readily be movedagainst the surface portion 96 of member 93-to hold the same withinrecess 92. As seen in FIG. 6, member 96 has a recess 115, which fitsaround bolt 106 in the closed position of the assembly.

The recessed portion of sides 108 adjacent apertures 114 is generallyrectangular and the sides 116 thereof adjacent nut 112 will act as arestraint upon rotation of the nut so that the tension onsides 108,produced between the nut 112 and the head 120, of bolt 106 may be"relieved simply by turning the bolt. To this end a handle 122 issecured to the head 120 in any convenient manner, to facilitate rotationof the bolt.

ln previously proposed clamping arrangements, the

the neeessity for cleaning arose. Since in many welding processes, thedistance from the tip of the torch to the weld joint is critical, it wasnecessary in such previously proposed welding head clamps to accuratelyand painstakingly readjust this distance on each cleaning of the weldingtorch. With applicants clamp as described above, this problem is avoidedsince the pivotal mounting of the welding torch 80 about pivot pin 94permits the welding torch to be selectively swung away from the joint 13in the event that cleaning of the tip thereof is required. Thus,cleaning of the tip can be accomplished without the necessity ofremoving the torch from the clamp itself.

It is also noted that collar 100 is at a slight angle with respect tothe axis of shaft 68 and thus is also at a slight angle a, generally 5with respect to the radius of a pipe being welded (see FIG. 3).,Thisfeature is advantageous since, as the assembly is moved by ring gear 16with the torch at the trailing end thereof, that is, the assembly ismoved to the left in FIG. 3 during the welding operation, the weldingforce, because of the angular mounting of the torch, will tend tosupport molten weld metal and eliminate sag in the weld, particularly inthe overhead positions.

The rear portion of plate 62, as seen in FIG. 3, provides mounting forthe motor 72. In addition, it is provided with a dependingplate 124 onwhich a guide arm 126 is pivotally mounted by pivot pin 128. Guide arm126 is a generally L-shaped member having an upstanding portion 130which abuts against plate 124. A bolt 132 is threadedly engaged throughleg 130 with plate 124 and is surrounded by a compression spring 134which biases the arm 126 in a generally clockwise direction as seen inthe drawing. The free end 136 of guide arm 126 is provided with a guidemember 138 which is adapted to be engaged in and follow the joint 13between the pipes 11 and 12 to be welded. The spring 134 and bolt 132serve to keep the guide member 138 within the joint during the weldingprocess. It is thus seen that as the assembly 10 is moved about theperiphery of pipes 11 and 12 during the welding process with guidemember 138 engaged within joint 13, the plate 62 will he slid laterallyby the guide arm 126 due to any lateral deviations of the joint 13. Inthis manner the welding torch is tracked with respect to the joint sothat its position with respect to the joint is held constant at alltimes.

ln the-preferred embodiment of the invention the clamp 78 is mounted inthe apparatus in a position such that the welding torch 80, at thecenter of its path of oscillation, is in substantial alignment with theguide member 138, as seen in FIG. 1, so that it oscillates with equalamplitude on either side of the centerline of the joint during thewelding process in spite of any deviations of the joint. Thiscombination of oscillating motion and sliding motion of the welding headis a substantial improvement over previously proposed arrangements andprovides for uniform welding of the joint about the entire periphery ofthe pipeline.

As mentioned, this apparatus is particularly adapted for use with thewelding process described in the above-mentioned U.S. patentapplication. in particular, this embodiment of the invention is utilizedin the root and filler passes of the welding system described therein.During these passes, the joint 13 between the pipeline is sufficientlydeep to permit the guide member 138 to track the joint. However, as the'last filler pass is made andthe head comes around the machine to thestarting point of the weld, there is insufficient joint side wallavailable for the guide member 138 to track. Thus, the possibilityresults that plate 62 will float" irradically, thereby causing thewelding head to move away from the joint during the last phase of thewelding process.

To avoid-this possibility, the welding apparatus of the presentinvention is provided with a solenoid 140 mounted in housing 60 onsupport plate 62. A metal brake bar 142 is rigidly secured to plate 26and extends through housing 60 adjacent solenoid 140. The cireuitryutilized to control the welding process is programmed such that as thewelding head approaches the last three inches of the last filler pass inthe welding process, the solenoid 140 is activated and it becomesmagnetically engaged with brake bar 142. This programming may be donewith conventional electronics or mechanically with cam operated switchesconnected to the ring gear. As a result, housing 60 and thus plate 62 isheld in a fixed position with respect to bar 142 and therefore withrespect to platform 52. The welding device then completes the last threeinches of the welding process with the plate 62 unable to move withrespect to the platform 52 and thus with welding head 80 in a fixedposition. It has been found that it is unlikely in the span of threeinches along the joint between pipelines that there would be sufficientvariation in the lateral location of the joint for there to be anysubstantial effect on the uniformity of the weld produced by the processdescribed in the above-mentioned patent application. The electronicsutilized to program the apparatus of the invention forms no part of theinvention and the construction of a circuit capable of performing thisfunction is within the skill of an artisan or a practicioner in the art.

Referring again to FIG. of the drawing, it is seen that the shaft 74 ofmotor 72 is provided with a notch 144 which is adapted to be engaged bya screwdriver for manually rotating the shaft. This end portion of theshaft extends through the forward face of housing 60, which housingencloses the gears 70, 76 and solenoid 140, so it is readily availablefor engagement and adjustment by a screwdriver. This adjustment isprovided so that the tip of a welding head mounted in the clampingassembly may be adjusted at the beginning of the welding operation to bein alignment with guide member 138, in the centerline of its path ofoscillation. This adjustment is assured by the provision of a pointer orindex means 146 on the top end 148 of shaft 68. The pointer is adaptedto be aligned with a dot 150, located in a predetermined position on thetop surface of housing 60, when the shaft 68 is in the position whereinit is at the centerline of its range of oscillation. Accordingly, byrotating shaft 74 and thus worm gear 76, the shaft 68 can be manuallyrotated until the pointer 146 aligns with the dot 150. It is also notedthat the provision of the spur gear 70 and worm gear 76 preventsinadvertent movement of the shaft 68, other than by the rotation of theshart 74 in the manner described, or by driving the shaft 74 by themotor 72.

With the welding head clamping assembly adjusted in this manner, thewelding operation may begin. The oscillation of the clamp and weldinghead is controlled by the logic circuit illustrated in block diagrams inFIG. 8. This circuit includes a step rate selector circuit 160 which isadapted to produce pulse signals at a preselected rate. This rate isselected by a conventional potentiometer connected to the circuit and isselected in accordance with the desired frequency of oscillation for thewelding head. Thus, the greater the frequency of the pulses, the greaterwill be the speed of oscillation of the welding head. The width oramplitude of the oscillations is controlled by the binary counter whichcounts a preselected number of pulses to be passed to motor 72 for eachoscillation. Thus, the greater the desired width, the greater the numberof pulses will be. This width is manually selected from width selectorswitch 162 which determines the number of pulses binary counter 164 willcount.

Since it is desirable to begin welding operations at the center of thejoint to be welded, the clamping assembly is adjusted as described aboveso that the welding torch is in the center of the joint. Thus it isnecessary to drive the welding torch first in one direction (S), forexample to the left in FIG. 1, half the number of pulses for thepreselected desired oscillation. To this end an on-off logic circuit 165is provided which is activated when the on-off switch 166 is turned on.At the initial portion of the operation, the step rate circuit isactivated to produce pulses at the preselected frequency and this signalis sent to the width logic circuit 168 and flip-flop 170. The widthlogic circuit is connected to binary counter 164 which normally countsthe predetermined number of pulses and, when this number is counted,returns a signal to the width logic circuit 168 instructing it toperform the next function. During the initial phase however, the signalfrom the width logic circuit controls the flip-flop 170, through logiccircuit 165, to permit only one half the desired number of pulses topass through the direction logic circuit 171 to the translator circuit173, which is preset to drive the motor in the first (or left)directions.

The pulses presented to the direction logic from step rate circuit 160pass through the direction logic only when it is closed by a signal fromthe on-off logic circuit 165 or from the delay 172. During the initialportion of the oscillation, the width logic 168 is controlled by theon-off logic circuit 166 which thus controls the number of pulsespermitted to pass through the direction logic. After the on-off logic isclosed, the width logic turns the direction logic off after one half ofthe preset width pulses are counted. During the remainder of theoperation the pulses produced by the step rate circuit 160 continue topass through direction logic 171 and are simultaneously counted bycounter 164. When the preselected number of pulses are counted, asdetermined by the desired oscillation width, the welding head is at theextreme end of its desired oscillation and the counter 164 sends asignal to the width logic circuit 168 which in turn activates the delay172 to open the gate and prevent further pulses from the step ratecircuit 160 from passing through the directional logic to the translatorand motor. The delay is held for a predetermined adjustable period, set,for example, by a potentiometer, so that the welding head is held at theend of its oscillation for a desired time period. This is often requiredin traveling welding operations, such as that described herein and inthe above-mentioned patent application, in order to accommodate thetravel speed of the mechanism.

After the delay period, the flip-flop is pulsed to change its outputstate. The flip-flop energizes the width logic which in turn activatesthe step rate. The flip-flop change in state also caused a change in thedirection logic so that the step rate pulses pass through the R lead tothe translator. This moves the weld torch in the R direction, forexample, to the right in FIG. 1, a number of pulses equal to the presentvalve on the width selector. The counter 164 sends a signal to the widthlogic circuit which in turn activates the delay 172 and turns off thepulses from the step rate. After the delay period the flip-flop is againpulsed to change its state. The flip-flop energizes the width logicwhich starts the step rate and changes the direction logic so that thepulse passes through the S lead to the translator.

The translator 173 between the direction logic and motor 72 in thecircuit illustrated in FIG. 8 in a conventional circuit utilized andsupplied as part of conventional stepping motors to'convert the pulsesignal to a usable sequence for the motor. A centering override 174 isprovided in order to manually drive the motor 72 to the center positionshould that be required.

At the end of the welding process, the on-off switch 166 is closed,however, the oscillation of the motor 72 is not immediately shut off andthe circuit continues in operation unitl the welding torch is stopped inits proper position. The torch must be stopped after it has moved halfway in the first direction mentioned above, i.e., in the direction ofmotion in which it will start again during the next operation. Thus, thedirection logic is wired to instruct the on-off circuit of the positionof the welding head during the welding oscillation and if the desiredstopping point has been passed, that is, if the welding head has movedpast the centerline,

in its leftward movement in FIG. 1, the on-off circuit is held on sothat the circuit remains in operation until the welding head is drivenback across the joint to the right and begun to move to the left again.Then after the delay and when the head begins moving leftward again, theon-off logic circuit and width logic circuit control the flip-flop topermit only half the predetermined number of pulses counted by thebinary counter to pass therethrough to the direction logic circuit sothat the welding head is only driven back half way, i.e., to the centerof the joint. In the event that the on-off switch is turned off duringthe delay period when the welding head is at the right of the joint asseen in FIG. 1, or as it is moving towards the center of the joint, butbefore it reaches the center of the joint, then the on-off logic circuitis designed to control the circuit to stop the motor when the weldinghead reaches the center of the joint.

The particular circuitry utilized in each of the blocks described inFIG. 8 of conventional construction and it is the combination of theseconventional circuits, as described above and as shown in the blockdiagram which is novel to applicants herein. Accordingly, the specificdetailed circuit diagram for each of these blocks is not required andthe above description and the circuit diagram of FIG. 8 is sufficientfor one skilled in the art to produce the circuit in accordance with theinvention.

It is contemplated that two welding head assemblies will besimultaneously used in performing the welding operation described in theabove-mentioned patent ap plication. These welding heads will be usedsimultaneously and in general will be located on opposite sides of thepipe being welded during the welding operation. When welding the rootandfiller passes, the welding heads are independently controlled since theyare tracked as described above by the guide member 126. However, whenthe cap pass is made, the welding heads cannot be independently tracked,since the weld joint will be substantially filled during the cap passand tracking of the weld head by the guide member 138 will beimpractical. Thus, when the welding head clamping and oscillatingassembly of the present invention is to be used to form the cap pass ofa welding operation as described in the above-mentioned patentapplication, some modification must be made thereto. Accordingly, amodified welding head I88 (FIG. 10) is provided for the cap pass whereinthe guide arm 126 and its associated equipment are eliminated. In lieuthereof, the support platform 52 is provided with a rack I89 rigidlysecured thereto. A reversible electric motor 190 (this motor replacesthe brake of the head oscillator) is be reciprocated with respect toplatform 52 on the rods 64.

As mentioned, the welding operation is performed with two welding heads(FIG. 12), each of which is mounted on a ring gear 16 by a connectingmechanism 14, similar to that described above. The ring gears arerotatably mounted on a common frame 190' and are driven about theperiphery of pipeline 11 by electric motors l8, shafts 20 and piniongears 22. Frame 190' is seated on pipeline 11 by at least one pair ofspaced rollers 193 (only one of which is shown) located at the left endof frame 190 and a pair of support arms 194 (note FIG. 13) which arevertically adjustable in frame 190. Support arms 194 have beveledsurfaces 195 which engage the outer surface of the in place pipe and areintegrally interconnected by a cross piece 196. The latter is mounted onthe frame 190' for vertical movement with respect thereto and isoperably engaged on its upper surface by a pair of screw jacks 197 whichare rotated by motor 198 on frame 190' through bevel gears 199 and wormgear 200. By this arrangement frame 190' may be tilted about rollers 193to adjust the relative position of frame 190' and thus ring gears 16with respect to the pipeline. This adjustment capability of the frame isutilized as more fully described hereinafter to align the torches inheads 188 with the groove 13 between the pipelines. To accomplish this,one of the heads 188 is provided with a guide pointer 20] (FIGS. 9 and12) pivotally secured by pivot pin 202 on extension 203 at the rear ofits plate 62. In the illustrative embodiment the lower head 188 shown inFIG. 12 is provided with pointer 201.

At the beginning of the cap pass welding operation, the pointer 201 ofthe lower head 188 is in its retracted position, seen in solid lines inFIG. 9, and the heads are moved into the positions shown. If the weldingtip 81 of torch in the upper head does not align with the center of thegroove, the operator operates the appropriate switch to activate itsmotor to drive plate 62 to a position wherein the end 81 of the weldingtorch is located at the middle of the welding groove l3. When that pointis reached, the motor 190 is deactivated and the plate 62 and thus torch80 is held in that position by the engagement of rack 190 and pinion196.

Safety limit switches 204 are positioned in spaced relation in theextension 203 of plate 62. These limit switches cooperate with anextension 206 on platform 52, which extension has a pair of bolts 208 orthe like secured therein for engagement with the limit switches 204.These switches control motor 190. and override the manual control whenthe plate 62 hasbeen driven to its extremes in either direction, asdetermined bythe spacing of switches 204. This arrangement provides asafety feature in the apparatus which avoids damage to the bearings andto the rack and pinion assembly. In the event that the operator isunable to align the welding torch with the center of the joint bymovement of plate 62 within the range defined by switches 204, then theentire welding mechanism including ring gear 16 must be moved intocloser alignment with the "joint in order to position the welding headadjacent the joint.

It has been found advantageous to electrically interconnect the motors190' of each of the heads 188 so that they will move simultaneously inopposite directions when the motors are activated. As a result, themotors 190 move their associated plates 62 and thus their torches 80simultaneously in opposite directions.

Thus, when torch 80 in the upper head 188 is moved to its centeredposition, the torch on the lower head will be moved in the opositedirection to a position in alignment with the first mentioned torchtowards the groove 13. That is, assuming the torch 80 in the upper headin FIG. 12 is out of alignment with groove 13, and on the right side ofthe groove, then the down torch will be on the left side of the groove.As the first torch is moved to the left towards the groove the lowertorch will move to the right, also towards the groove. Thus, when thetop torch tip is aligned with the groove, the lower torch tip should besimilarly aligned. To check this alignment, guide pointer 200 on thelower head is moved to its dotted line position as shown in FIG. 9. Thepointer is mounted in alignment with the torch tip and its end 203 willbe diametrically located with respect to torch tip 81 of the upper headwhen the heads are in the position shown in FIG. 12. In the event thatend 203 does not align with groove 13, because, for example, the grooveis at an angle to the longitudinal axis of the pipeline, the motor 198can be operated to drive jacks 197, thereby causing the right end offrame 190' to rise with respect to supports 194 so that the frame istilted. Motor 198 is operated until the frame is tilted about rollers193 to a position wherein the end 203' of the pointer is in the groove.Generally, only a slight tilt of frame 190' is required, and since thetip 81 of the upper torch is closer to the pivot axis than the tip ofthe lower head, tip 81 remains essentially stationary and located withinthe confines of the groove. In this manner, the plane of travel of theheads is made to coincide with the plane of the groove or joint 13.After the adjusting operation is completed, both assemblies then remainfixed, due to the engagement of racks 189 with pinion 192, and, whenrotated simultaneously, will follow the joint between the pipes as theirrespective torches are oscillated by motors 72.

Although illustrative embodiments of the present invention have beendescribed herein with reference to the assompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments and that various changes and modifications may be effectedtherein by one skilled in the art without departing from the scope orspirit of this invention.

What is claimed is:

l. A welding head clamping and oscillating assembly for use in a weldingmachine having means for supporting and moving said assembly along ajoint to be welded, said assembly comprising, a support platform, meansfor connecting said support platform to the assembly supporting means ofa welding machine, a support plate freely slidably mounted on saidsupport platform for reciprocal movement in a direction transverse tosaid joint, a welding head clamp means pivotally mounted on said supportplate for arcuate oscillating movement in a plane extendingsubstantially parallel to said support plate and in a directionsubstantially parallel to the direction of the slidable mounting of saidsupport plate and transversely of said joint, a reversible steppingmotor operatively connected to said clamp for oscillating the clampabout its pivot axis; and a guide arm mounted on said plate andextending therefrom to a position below said platform, said guide armhaving a guide member adapted to be positioned in said joint to bewelded to track said joint as the assembly is moved therealong by saidsupporting and moving means whereby said plate is moved with respect tosaid platform in response to variations in the lateral locations of saidjoint.

2. The welding head clamping and oscillating assembly as defined inclaim 1 including a pivot shaft rotatably mounted at one end in saidplate and extending generally perpendicularly thereto, and a spur gearrigidly scured to said shaft, said stepping motor having an output shaftextending perpendicularly to said pivot shaft and a worm gear secured tothe end of said output shaft in meshing engagement with said spur gearfor oscillating said pivot shaft and said welding head clamp beingrigidly secured to said pivot shaft for oscillation therewith.

3. The welding head clamping and oscillating assembly as defined inclaim 2 wherein said stepping motor shaft has a free end extendingbeyond said worm gear and includes means at said free end for manuallyrotating said shaft whereby the position of said clamp may be manuallyadjusted.

4. The welding head clamping and oscillating assembly as defined inclaim 3 including a housing mounted on said plate and enclosing saidpivot shaft and stepping motor output shaft, said free end of saidoutput shaft and the other end of said pivot shaft extending throughsaid housing, index means on said other end of the pivot shaft and indexmeans on said housing adjacent said pivot shaft, said index means beingrespectively located to be adjacent each other when said clamping headis in position intermediate the ends of its path of oscillation.

5. The welding head clamping and oscillating assembly as defined inclaim 2 including at least two cylindrical rods mounted in said supportplatform and a pair of elongated bearing members mounted on said platerespectively receiving said rods for slidably mounting said supportplate on said platform.

6. The welding head clamping and oscillating assembly as defined inclaim 1 wherein said clamp and said guide member are mounted on saidplatform with respect to each other in relative positions wherein thecentral point of the path of oscillation of said clamp corresponds tothe center of said guide member whereby a welding head in said clampwill oscillate with equal amplitude on either side of said joint to bewelded as the position of said support plate varies in response to thetracking of said guide member in said joint.

7. The welding head clamping and oscillating assembly as defined inclaim 6 wherein said guide arm is pivotally mounted on said plate alonga straight axis parallel to the path of sliding movement of said supportplate, and said assembly includes means for biasing said arm downwardlywith respect to said plate to maintain said guide member in said joint.

8. The welding head clamping and oscillating assembly as defined inclaim 2 wherein said welding head clamp comprises first and secondpivotally interconnected members, said first member having a recess onone side thereof which is adapted to receive said second member and asplit ring collar on the other side thereof and integral therewith forreceiving said pivot shaft, and means for rigidly clamping said collarabout said pivot shaft, said second member having a split collarintegral therewith on the side thereof opposite said first member forreceiving a welding head and means for rigidly clamping said collarabout a welding head inserted therein.

9. The welding head clamping and oscillating assembly as defined inclaim 8 including means for clampingly engaging the sides of said firstmember which define said recess with the portion of said second memberreceived therein for selectively preventing pivotal movement of saidsecond member with respect to said first member.

10. The welding head clamping and oscillating assembly as defined inclaim 9 wherein the central axis of said split collar receiving awelding head is in the same plane as and at a slight angle to the axisof said pivot shaft.

11. The welding head clamping and oscillating as sembly as defined inclaim 1 wherein said means for connecting said platform to said assemblysupporting means comprises a first plate adapted to be rigidly connectedto said assembly supporting means and having a dove-tail flange on theside thereof opposite said supporting means, said flange extendinggenerally perpendicularly of said supporting platform, a second platerigidly secured to said platform and having a dove-tail recess adaptedto slidably receive said flange, and means slidably mounted in saidfirst plate and rigidly connected to said second plate for holding saidflange in said recess while permitting relative movement between saidfirst arid second plates, whereby said welding head clamping andoscillating assembly is mounted on said supporting assembly and isrelatively movable with respect thereto.

12. The welding head clamping and oscillating assembly as defined inclaim 11 wherein said means connecting said first and second platescomprises an elongated rod slidably mounted on said first plate adjacentsaid flange and having a threaded end threadedly engaged with a bossrigidly secured to said second plate, a nut on said threaded end remotefrom the free end thereof, and spring means surrounding said rod andoperative between said nut and said first plate to bias said rod andsaid platform downwardly towards the joint to be welded. I

13. The welding head clamping and oscillating assembly as defined inclaim 12 wherein said platform includes a guide wheel rotatably mountedthereon along an axis substantially perpendicular to the path of travelof said assembly, said guide wheel being adapted to engage the surfaceof an adjacent workpiece and cooperate with said spring to maintain saidplatform and the welding mead mounted thereon a predetermined distancefrom the surface of said workpiece.

14. The welding head clamping and oscillating assembly as defined'inclaim 13 wherein the axis of rotation of said wheel extendsperpendicularly to said rod and lies in a common plane therewith.

15. The welding head clamping and oscillating assembly as defined inclaim 1 including a metal brake bar rigidly secured to said platform anda selectively activated electrical solenoid rigidly mounted on saidsupport plate in closely spaced relation to said brake bar, saidsolenoid being adapted, when activated, to attract and hold said brakebar in fixed position with respect thereto whereby said support plate isheld against movement with respect to said support platform.

16. The welding head clamping and oscillating assembly as defined inclaim 1 including a rack gear mounted on said support platform and aselectively operable reversible electrical motor mounted on said supportplate, said reversible electrical motor having an output shaft and apinion mounted on the free end thereof for cooperation with said rackgear whereby the relative position of said support plate with respect tosaid platform may be varied by operation of said reversible electricmotor.

17. A welding head clamping and oscillating assembly for use in awelding machine having means for supporting and moving said assemblyalong a joint to be welded, said assembly comprising, a supportplatform, means for connecting said support platform to the assemblysupporting means of a welding machine, a support plate freely slidablymounted on said support platform for reciprocal movement in a directiontransverse to said joint, a welding head clamp means pivotally mountedon said support plate for arcuate oscillating movement in a planeextending substantially parallel to said support plate and in adirection substantially parallel to the direction of the slidablemounting of said support plate and transversely of said joint, areversible stepping motor operatively connected to said clamp foroscillating the clamp about its pivot axis; a rack gear mounted on saidsupport platform and a selectively operable reversible electrical motormounted on said support plate, said reversible electrical motor havingan output shaft and a pinion mounted on the free end thereof forcooperation with said rack gear whereby the relative position of saidsupport plate with respect to said platform may be varied by operationof said reversible motor; and an alignment guide pivotally mounted onsaid support plate on the side thereof opposite said welding head clamp,in alignment therewith and lying in a common plane with the tip of awelding head and mounted in said clamp, said guide comprising meansmovable from a first retracted position adjacent said support plate toan extended position wherein the free end thereof is adapted to belocated adjacent to the joint to be welded.

18. The welding head clamping and oscillating assembly as defined inclaim 17 including a pair of spaced limit switches mounted on said plateand connected to said reversible electrical motor to selectively stopsaid motor, and engagement means mounted on said support platformbetween said limit switches and located in the same plane as saidalignment guide and welding head tip, for selectively actuating saidlimit switches when engaged therewith as said plate is moved withrespect to said platform, thereby to define a limited path of travelover which said support plate may be moved by said reversible electricmotor. I

19. A welding head clamping and oscillating assembly for use in awelding maching having means for supporting and moving said assemblyalonga joint to be welded, said assembly comprising, a support platform,means for connecting said platfonn to the assembly supporting means of awelding machine, a support plate freely slidably mounted on said supportplatform for reciprocal movement in a direction transverse to saidjoint, a pivot shaft rotatably mounted on said support plate andextending generally perpendicularlythereto, a spur gear rigidly securedto said shaft, a reversible stepping motor mounted on said plate andhaving an output shaft extending perpendicularly to said pivot shaft anda wonn gear secured to the end of said output shaft in meshingengagement with said spur gear whereby said pivot shaft is adapted to beoscillated about its axis of rotation by said stepping motor, a weldinghead clamp rigidly connected to said pivot shaft for arcuate oscillationtherewith in a plane extending substantially parallel to said supportplate and in a direction substantially parallel to the direction ofsliding movement of said support plate and transverse to said joint, aguide arm mounted on said plate and extending therefrom to a positionbelow said platform, said guide arm having a guide member adapted to bepositioned in a joint to be welded and located on said guide arm to bein a common plane with the tip of a welding head mounted in said clampwhen said clamp is at the central point of its path of oscillation, saidguide member comprising means tracking in the joint to be welded as theassembly is moved therealong by said supporting and moving means, tomove said support plate with respect to said platform in response tovariations in the lateral locations of said joint whereby a welding headin said clamp will oscillate in a relatively flat plane above said jointand with equal amplitude on either side of said joint to be weldedduring the welding process 20. The welding head clamping and oscillatingassembly as defined in claim 19 wherein said guide arm is pivotallymounted on said plate along a straight axis parallel to the path ofsliding movement of said support plate and said assembly includes meansfor biasing said arm downwardly with respect to said plate to maintainsaid guide member in said joint.

21. The welding head clamping and oscillating assembly as defined inclaim 20 including a metal brake bar rigidly secured to said platformand a selectively activated electrical solenoid rigidly mounted on saidsupport plate in closely spaced relation to said brake bar, saidsolenoid being adapted, when activated, to attract and hold said brakebar in fixed position with respect thereto whereby said support plate isheld against movement with respect to said support platform.

22. A welding head clamping and oscillating assembly for use in awelding machine having means for supporting and moving said assemblyalong a joint to be welded, said assembly comprising, a supportplatform, means for connecting said support platform to the assemblysupporting means of a welding machine, a support plate freely slidablymounted on said support platform for reciprocal movement in a directiontransverse to said joint, a pivot shaft rotatably mounted on saidsupport plate and extending generally perpendicularly thereto, a spurgear rigidly secured to said shaft, a reversible stepping motor havingan output shaft extending perpendicularly to said pivot shaft and a wormgear secured to the end of said output shaft in meshing engagement withsaid spur gear whereby said pivot shaft is adapted to be oscillatedabout its axis of rotation by said stepping motor, a welding head clamprigidly connected to said pivot shaft for oscillation therewith in aplane extending substantially parallel to said support plate and in adirection substantially parallel to the direction of sliding movement ofsaid support plate and transverse to said joint, a rack gear mounted onsaid support platform and a selectively operable reversible electricalmotor mounted on said support plate, said reversible electrical motorhaving an output shaft and a spur gear mounted on the free end thereoffor cooperation with said rack gear whereby the relative position ofsaid support plate with respect to said platform may be varied by theoperation of said reversible electric motor; and an alignment guidepivotally mounted on said support plate on the side thereof oppositesaid welding head clamp and in alignment therewith, and wherein saidalignment guide lies in a common plane with the tip of a welding headmounted in said clamp, said guide comprising means movable from a firstretracted position adjacent said support plate to an extended positionwherein the free end thereof is adapted to be located adjacent to thejoint to be welded.

23. The welding head clamping and oscillating assembly as defined inclaim 22 including a pair of spaced limit switches mounted on said plateand connected to said reversible electrical motor to selectively stopsaid motor, and engagement means mounted on said support platformbetween said limit switches and located in the same plane as saidalignment guide and welding head tip, for selectively actuating saidlimit switches when engaged therewith as said plate is moved withrespect to said platform, thereby to define a limited path of travelover which said support plate may be moved by said reversible electricmotor.

1. A welding head clamping and oscillating assembly for use in a weldingmachine having means for supporting and moving said assembly along ajoint to be welded, said assembly comprising, a support platform, meansfor connecting said support platform to the assembly supporting means ofa welding machine, a support plate freely slidably mounted on saidsupport platform for rEciprocal movement in a direction transverse tosaid joint, a welding head clamp means pivotally mounted on said supportplate for arcuate oscillating movement in a plane extendingsubstantially parallel to said support plate and in a directionsubstantially parallel to the direction of the slidable mounting of saidsupport plate and transversely of said joint, a reversible steppingmotor operatively connected to said clamp for oscillating the clampabout its pivot axis; and a guide arm mounted on said plate andextending therefrom to a position below said platform, said guide armhaving a guide member adapted to be positioned in said joint to bewelded to track said joint as the assembly is moved therealong by saidsupporting and moving means whereby said plate is moved with respect tosaid platform in response to variations in the lateral locations of saidjoint.
 2. The welding head clamping and oscillating assembly as definedin claim 1 including a pivot shaft rotatably mounted at one end in saidplate and extending generally perpendicularly thereto, and a spur gearrigidly scured to said shaft, said stepping motor having an output shaftextending perpendicularly to said pivot shaft and a worm gear secured tothe end of said output shaft in meshing engagement with said spur gearfor oscillating said pivot shaft and said welding head clamp beingrigidly secured to said pivot shaft for oscillation therewith.
 3. Thewelding head clamping and oscillating assembly as defined in claim 2wherein said stepping motor shaft has a free end extending beyond saidworm gear and includes means at said free end for manually rotating saidshaft whereby the position of said clamp may be manually adjusted. 4.The welding head clamping and oscillating assembly as defined in claim 3including a housing mounted on said plate and enclosing said pivot shaftand stepping motor output shaft, said free end of said output shaft andthe other end of said pivot shaft extending through said housing, indexmeans on said other end of the pivot shaft and index means on saidhousing adjacent said pivot shaft, said index means being respectivelylocated to be adjacent each other when said clamping head is in positionintermediate the ends of its path of oscillation.
 5. The welding headclamping and oscillating assembly as defined in claim 2 including atleast two cylindrical rods mounted in said support platform and a pairof elongated bearing members mounted on said plate respectivelyreceiving said rods for slidably mounting said support plate on saidplatform.
 6. The welding head clamping and oscillating assembly asdefined in claim 1 wherein said clamp and said guide member are mountedon said platform with respect to each other in relative positionswherein the central point of the path of oscillation of said clampcorresponds to the center of said guide member whereby a welding head insaid clamp will oscillate with equal amplitude on either side of saidjoint to be welded as the position of said support plate varies inresponse to the tracking of said guide member in said joint.
 7. Thewelding head clamping and oscillating assembly as defined in claim 6wherein said guide arm is pivotally mounted on said plate along astraight axis parallel to the path of sliding movement of said supportplate, and said assembly includes means for biasing said arm downwardlywith respect to said plate to maintain said guide member in said joint.8. The welding head clamping and oscillating assembly as defined inclaim 2 wherein said welding head clamp comprises first and secondpivotally interconnected members, said first member having a recess onone side thereof which is adapted to receive said second member and asplit ring collar on the other side thereof and integral therewith forreceiving said pivot shaft, and means for rigidly clamping said collarabout said pivot shaft, said second member having a split collarintegral therewith on the side thereof opposite said first member forreceiving a welDing head and means for rigidly clamping said collarabout a welding head inserted therein.
 9. The welding head clamping andoscillating assembly as defined in claim 8 including means forclampingly engaging the sides of said first member which define saidrecess with the portion of said second member received therein forselectively preventing pivotal movement of said second member withrespect to said first member.
 10. The welding head clamping andoscillating assembly as defined in claim 9 wherein the central axis ofsaid split collar receiving a welding head is in the same plane as andat a slight angle to the axis of said pivot shaft.
 11. The welding headclamping and oscillating assembly as defined in claim 1 wherein saidmeans for connecting said platform to said assembly supporting meanscomprises a first plate adapted to be rigidly connected to said assemblysupporting means and having a dove-tail flange on the side thereofopposite said supporting means, said flange extending generallyperpendicularly of said supporting platform, a second plate rigidlysecured to said platform and having a dove-tail recess adapted toslidably receive said flange, and means slidably mounted in said firstplate and rigidly connected to said second plate for holding said flangein said recess while permitting relative movement between said first andsecond plates, whereby said welding head clamping and oscillatingassembly is mounted on said supporting assembly and is relativelymovable with respect thereto.
 12. The welding head clamping andoscillating assembly as defined in claim 11 wherein said meansconnecting said first and second plates comprises an elongated rodslidably mounted on said first plate adjacent said flange and having athreaded end threadedly engaged with a boss rigidly secured to saidsecond plate, a nut on said threaded end remote from the free endthereof, and spring means surrounding said rod and operative betweensaid nut and said first plate to bias said rod and said platformdownwardly towards the joint to be welded.
 13. The welding head clampingand oscillating assembly as defined in claim 12 wherein said platformincludes a guide wheel rotatably mounted thereon along an axissubstantially perpendicular to the path of travel of said assembly, saidguide wheel being adapted to engage the surface of an adjacent workpieceand cooperate with said spring to maintain said platform and the weldingmead mounted thereon a predetermined distance from the surface of saidworkpiece.
 14. The welding head clamping and oscillating assembly asdefined in claim 13 wherein the axis of rotation of said wheel extendsperpendicularly to said rod and lies in a common plane therewith. 15.The welding head clamping and oscillating assembly as defined in claim 1including a metal brake bar rigidly secured to said platform and aselectively activated electrical solenoid rigidly mounted on saidsupport plate in closely spaced relation to said brake bar, saidsolenoid being adapted, when activated, to attract and hold said brakebar in fixed position with respect thereto whereby said support plate isheld against movement with respect to said support platform.
 16. Thewelding head clamping and oscillating assembly as defined in claim 1including a rack gear mounted on said support platform and a selectivelyoperable reversible electrical motor mounted on said support plate, saidreversible electrical motor having an output shaft and a pinion mountedon the free end thereof for cooperation with said rack gear whereby therelative position of said support plate with respect to said platformmay be varied by operation of said reversible electric motor.
 17. Awelding head clamping and oscillating assembly for use in a weldingmachine having means for supporting and moving said assembly along ajoint to be welded, said assembly comprising, a support platform, meansfor connecting said support platform to the assembly supporting means ofa welding machine, a suppoRt plate freely slidably mounted on saidsupport platform for reciprocal movement in a direction transverse tosaid joint, a welding head clamp means pivotally mounted on said supportplate for arcuate oscillating movement in a plane extendingsubstantially parallel to said support plate and in a directionsubstantially parallel to the direction of the slidable mounting of saidsupport plate and transversely of said joint, a reversible steppingmotor operatively connected to said clamp for oscillating the clampabout its pivot axis; a rack gear mounted on said support platform and aselectively operable reversible electrical motor mounted on said supportplate, said reversible electrical motor having an output shaft and apinion mounted on the free end thereof for cooperation with said rackgear whereby the relative position of said support plate with respect tosaid platform may be varied by operation of said reversible motor; andan alignment guide pivotally mounted on said support plate on the sidethereof opposite said welding head clamp, in alignment therewith andlying in a common plane with the tip of a welding head and mounted insaid clamp, said guide comprising means movable from a first retractedposition adjacent said support plate to an extended position wherein thefree end thereof is adapted to be located adjacent to the joint to bewelded.
 18. The welding head clamping and oscillating assembly asdefined in claim 17 including a pair of spaced limit switches mounted onsaid plate and connected to said reversible electrical motor toselectively stop said motor, and engagement means mounted on saidsupport platform between said limit switches and located in the sameplane as said alignment guide and welding head tip, for selectivelyactuating said limit switches when engaged therewith as said plate ismoved with respect to said platform, thereby to define a limited path oftravel over which said support plate may be moved by said reversibleelectric motor.
 19. A welding head clamping and oscillating assembly foruse in a welding maching having means for supporting and moving saidassembly along a joint to be welded, said assembly comprising, a supportplatform, means for connecting said platform to the assembly supportingmeans of a welding machine, a support plate freely slidably mounted onsaid support platform for reciprocal movement in a direction transverseto said joint, a pivot shaft rotatably mounted on said support plate andextending generally perpendicularly thereto, a spur gear rigidly securedto said shaft, a reversible stepping motor mounted on said plate andhaving an output shaft extending perpendicularly to said pivot shaft anda worm gear secured to the end of said output shaft in meshingengagement with said spur gear whereby said pivot shaft is adapted to beoscillated about its axis of rotation by said stepping motor, a weldinghead clamp rigidly connected to said pivot shaft for arcuate oscillationtherewith in a plane extending substantially parallel to said supportplate and in a direction substantially parallel to the direction ofsliding movement of said support plate and transverse to said joint, aguide arm mounted on said plate and extending therefrom to a positionbelow said platform, said guide arm having a guide member adapted to bepositioned in a joint to be welded and located on said guide arm to bein a common plane with the tip of a welding head mounted in said clampwhen said clamp is at the central point of its path of oscillation, saidguide member comprising means tracking in the joint to be welded as theassembly is moved therealong by said supporting and moving means, tomove said support plate with respect to said platform in response tovariations in the lateral locations of said joint whereby a welding headin said clamp will oscillate in a relatively flat plane above said jointand with equal amplitude on either side of said joint to be weldedduring the welding process.
 20. The welding head clamping andoscillating asseMbly as defined in claim 19 wherein said guide arm ispivotally mounted on said plate along a straight axis parallel to thepath of sliding movement of said support plate and said assemblyincludes means for biasing said arm downwardly with respect to saidplate to maintain said guide member in said joint.
 21. The welding headclamping and oscillating assembly as defined in claim 20 including ametal brake bar rigidly secured to said platform and a selectivelyactivated electrical solenoid rigidly mounted on said support plate inclosely spaced relation to said brake bar, said solenoid being adapted,when activated, to attract and hold said brake bar in fixed positionwith respect thereto whereby said support plate is held against movementwith respect to said support platform.
 22. A welding head clamping andoscillating assembly for use in a welding machine having means forsupporting and moving said assembly along a joint to be welded, saidassembly comprising, a support platform, means for connecting saidsupport platform to the assembly supporting means of a welding machine,a support plate freely slidably mounted on said support platform forreciprocal movement in a direction transverse to said joint, a pivotshaft rotatably mounted on said support plate and extending generallyperpendicularly thereto, a spur gear rigidly secured to said shaft, areversible stepping motor having an output shaft extendingperpendicularly to said pivot shaft and a worm gear secured to the endof said output shaft in meshing engagement with said spur gear wherebysaid pivot shaft is adapted to be oscillated about its axis of rotationby said stepping motor, a welding head clamp rigidly connected to saidpivot shaft for oscillation therewith in a plane extending substantiallyparallel to said support plate and in a direction substantially parallelto the direction of sliding movement of said support plate andtransverse to said joint, a rack gear mounted on said support platformand a selectively operable reversible electrical motor mounted on saidsupport plate, said reversible electrical motor having an output shaftand a spur gear mounted on the free end thereof for cooperation withsaid rack gear whereby the relative position of said support plate withrespect to said platform may be varied by the operation of saidreversible electric motor; and an alignment guide pivotally mounted onsaid support plate on the side thereof opposite said welding head clampand in alignment therewith, and wherein said alignment guide lies in acommon plane with the tip of a welding head mounted in said clamp, saidguide comprising means movable from a first retracted position adjacentsaid support plate to an extended position wherein the free end thereofis adapted to be located adjacent to the joint to be welded.
 23. Thewelding head clamping and oscillating assembly as defined in claim 22including a pair of spaced limit switches mounted on said plate andconnected to said reversible electrical motor to selectively stop saidmotor, and engagement means mounted on said support platform betweensaid limit switches and located in the same plane as said alignmentguide and welding head tip, for selectively actuating said limitswitches when engaged therewith as said plate is moved with respect tosaid platform, thereby to define a limited path of travel over whichsaid support plate may be moved by said reversible electric motor.